Page 16 - ITAtube Journal 1 2022

Technical Papers
Andrew Houghton
Cold Pilger Tooling Design Key Steps
Fig. 2 Longitudinal Profile
16
Fig. 1 CAD View
The principle
Those familiar with pilger tooling will know that generally there are two ring or half ring dies positioned above each other
in a housing so that they can be moved backward and forward over the tube. This imparts a roll profile on the outside of the tube in a progressive manner. Each time the rolls go backward and forward the tube is fed into the roll pinch incrementally. Tube emerges with a smaller diameter and a thinner wall.
There is an equal and opposite profile ground into the circumference of each die and usually there is a mandrel inside the tube with a profile that controls the tube ID and wall thickness.
The fundamental issue is to decide the lon- gitudinal and transverse profile in what has to be a tapered groove in the roll. A coor- dinated mandrel longitudinal profile is also critical to success as both roll and mandrel together control the strain path.
So, the CAD drawing in Fig 1. shows a typical profile in a single ring die and the Graph in Fig 2. shows a plot in blue of the whole longitudinal die profile measured between the bottom of both opposed grooves through the machine centre line. The red line represents the mandrel diam- eter. A critical point between these rolls is at the ‘C’ point. This is nominally where the tooling dimensions will produce the desired tube size. The ‘C’point is at position ‘0.000’ on the horizontal axis on Fig 2.
As well as the longitudinal profile there is an equally important transverse profile which is nominally the radius of the tube but also has key elements of ‘side relief’ which is needed to allow the extending tube to fit into the groove as it progresses forward. It is also needed to accommodate the roll separation under load which pro- duces a larger diameter than initially calcu- lated. A critical measurement which can not
ITAtube Journal April 2022